Atomic layer deposition apparatus

ABSTRACT

The present invention relates to an ALD apparatus, and particularly relates to an ALD apparatus that is suitable for rapidly depositing a thin film on a substrate having an actual area that is larger than a planar substrate. In the reaction chamber of the ALD apparatus according to an exemplary embodiment of the present invention, more gas is supplied to a portion where more gas is required by having differences in the space for gas to flow rather than supplying the gas in a constant flux and a constant flow velocity such that the time required for supplying reactant gases and waste of reactant gases may be minimized to increase productivity of the ALD apparatus. The ceiling of the reaction space is shaped to provide a nonuniform gap over the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean PatentApplication No. 10-2006-0091412 filed in the Korean IntellectualProperty Office on Sep. 20, 2006, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an atomic layer deposition (ALD)apparatus, and particularly relates to an ALD apparatus that is suitablefor rapidly depositing a thin film on a structure having a larger actualarea than an apparent area, such as DRAM.

2. Description of the Related Art

In the manufacture of semiconductor devices, efforts for improvingapparatuses and processes to be suitable for forming a high quality thinfilm on a substrate have continued. In ALD methods, separate pulses ofat least two reactants are sequentially introduced on the substrate, asurface reaction of the reactants occurs to form a monolayer on thesurface of the substrate, and the reactants are sequentially introduceduntil a desired thickness of the deposited material is deposited. Inpure ALD methods, the reactants are pulsed separately, and temperaturesare kept in a window above condensation and below thermal decomposition,the thin film is formed by saturative surface reactions, and thereby athin film having a uniform thickness may be formed on the whole surfaceof the substrate regardless of surface roughness of the substrate andimpurities in the thin film may be reduced to form a thin film havinghigh quality.

A lateral flow ALD reaction chamber, in which gases flow laterally overand parallel to the major surface of a substrate, has been proposed. Inthe lateral flow ALD reaction chamber, flowing of the gases is rapid andsimple and thereby high speed switching of gas supplies may be attainedto reduce time required for sequentially supplying process gases.Exemplary lateral flow reaction chambers suitable for time-divided gassupply of an ALD method and a method of depositing a thin film using thelateral flow reaction chamber have been disclosed in Korean PatentApplication Nos. 1999-0023078 and 2000-0033548, and U.S. Pat. No.6,539,891. In addition, an improved example of the lateral flow reactionchamber suitable for time-divided gas supply of an ALD method and amethod of depositing a thin film using the lateral flow reaction chamberhave been disclosed in Korean Patent Application No. 2005-0038606 andU.S. patent application Ser. No. 11/429,533, published as U.S.Publication No. 2006-0249077 A1 on Nov. 9, 2006. Other examples oflateral flow ALD reaction chambers have been disclosed in U.S. Pat. No.5,711,811 and U.S. Pat. No. 6,562,140. In the examples, the reactionchambers have a constant gap between the side on which a substrate isdisposed and the side facing a surface of the substrate, such that gasflowing to the substrate may be constant and maintained in a state of anear laminar flow. such lateral flow reaction chambers are also referredto in the art as cross-flow or horizontal flow reaction chambers,although the orientation need not be horizontal.

A substrate with a rough surface having a plurality of protrusions anddepressions has an actual surface area that is larger than a planarsurface. In addition, in a dynamic random access memory (DRAM), adielectric layer that stores charge and has a plurality of thin holesand drains may have an actual surface area of about fifty times as largeas a planar substrate. Similarly, other integrated circuit patterns mayhave dense and/or high aspect ratio features that greatly increasesurface area relative to planar surfaces.

In general, a substrate or wafer for a semiconductor integrated circuitmay have a round planar shape.

If a substrate with a rough surface having an actual surface area ofabout fifty times as large as a planar substrate is set in a lateralflow ALD reaction chamber in which reactant gases supplied in a constantflux and a constant flow velocity, then the reactant gases supplied in aconstant flux and a constant flow velocity on the substrate may beconsumed in a different way relative to ALD on other substrates that donot have a rough surface. Accordingly, a gas supply of a constant fluxand a constant flow velocity may not be optimal for the substrate with arough surface having an actual surface area of about fifty times aslarge as a planar surface on a similar substrate, in that time requiredfor a saturative gas supply cycle may be longer and the amount of gasesrequired for the saturative gas supply cycle may be larger thanoptimally required.

In FIG. 1, a lateral flow ALD reaction chamber in which gases flow inthe direction of the arrows, and a circular substrate set in the lateralflow reaction chamber, are shown schematically. Referring to FIG. 1, ifthe gases are supplied to the reaction chamber in a gas pulse flow in aconstant flux and a constant flow velocity on the circular substratewith a rough surface having the actual surface area that is much largerthan a planar substrate, portions of the gases are consumed in positions300X, 300Y, and 300Z through adsorption or surface reaction on thesurface of the substrate after portions of the gases are consumedthrough adsorption or surface reaction on the surface of the reactionchamber. Even though adsorption or surface reaction on the surface ofthe substrate in the positions 300X, 300Y, and 300Z is completed,adsorption or surface reaction on the surface of the substrate in aposition 300W may not yet be completed, i.e., saturation may not beachieved. Accordingly, the gases must be supplied to the reactionchamber until adsorption or surface reaction on the surface of thesubstrate in a position 300W is completed. Thereby, the gases that flowon the positions 300X and 300Y after completion of adsorption or surfacereaction in the positions 300X and 300Z and before completion ofadsorption or surface reaction in the position 300W is excess andwasted. In other words, in order to achieve true surface saturation inall locations, full gas flow must be supplied to all locations until thelast-to-saturate location is saturated.

If reactant gases have enough vapor pressure and an excess of reactantgases is supplied to the reaction chamber, these differences ordifferent locations on the substrate may be ignored. For example, oxygen(O₂) gas or ozone (O₃) gas may be supplied at a much larger quantitycompared with the minimum quantity required to form a thin film, suchthat differences in rates of saturation at different positions on thesubstrate may be ignored. However, it takes a great deal of time tosupply a reactant gas having a lower vapor pressure such astetrakis(ethylmethylamido)halfnium (TEMAHf) ortetrakis(ethylmethylamido)zirconium (TEMAZr), which are often employedto form a thin film of HfO₂ or ZrO₂. The same is true of numerous otherprecursors, including metal halides and metalorganics, that are suitablefor ALD but have very low vapor pressures (e.g., less than about 0.1mmHg) under standard (room temperature and atmospheric pressure)conditions.

For example, if a circular substrate having a diameter of about 300 mmand having the actual surface area about fifty times as large as aplanar surface of 300 mm diameter is used, the time required forsupplying the reactant gas until completion of adsorption or surfacereaction on the whole surface of the substrate may be one second ormore.

In addition, if the reactant gas supplied to the reaction chamber is notused to form a thin film but passes through the reaction chamber, alonger time is required for supplying the reactant gas until completionof saturative adsorption or surface reaction on the whole surface of thesubstrate.

Accordingly, in order to reduce the time required for supplying thereactant gas with a lower vapor pressure and/or in order to reduce theconsumption of an expensive reactant gas, it is preferred thatadsorption or surface reaction on the whole surface of the substrate iscompleted, or the surface saturated, with minimum supply of the lowvapor pressure gas or the expensive gas.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The embodiments described herein provide an ALD apparatus including alateral flow ALD reaction chamber having advantages of reducing the timerequired for supplying reactant gases and waste of reactant gases in thecase of using a circular substrate having an actual surface area that ismuch larger than a planar surface would have on a similarly sizedsubstrate.

In one aspect, a lateral flow atomic layer deposition (ALD) apparatus inwhich reactant gases flow in a gas flow direction substantially parallelto a surface of a substrate includes a reaction chamber and a substratesupport configured for positioning the substrate within the reactionchamber. The apparatus also includes a part of the reaction chamberfacing the substrate support, with a portion depressed away from thesubstrate support. The substrate support and the reaction chamber partfacing it define a gas flow space above the substrate that is notuniform in height across a direction perpendicular to the gas flowdirection.

In another aspect, a method of conducting atomic lay deposition (ALD)includes providing a substrate in a reaction chamber. At least two ALDreactants are alternately and sequentially supplied into the reactionchamber space over the substrate in a gas flow direction parallel to thesubstrate, wherein the reaction space has a height over a center of thesubstrate greater than a height over edges of the substrate in across-sectional view perpendicular to the gas flow direction.

The depressed portion of the reaction chamber part may correspond to amiddle portion of the substrate when positioned on the substratesupport.

The maximum gap in which the reactant gas flows, between the substrateand the reaction chamber side, may be at least one and a half timeslarger than the minimum gap thereof.

The maximum gap in which the reactant gas flows within the reactionchamber, between the substrate and the reaction chamber side, may be atleast two times larger than the minimum gap thereof.

The minimum gap in which the reactant gas flows within the reactionchamber, between the substrate and the reaction chamber side, may beabout 0.5 mm to about 5 mm.

The minimum gap in which the reactant gas to flows within the reactionchamber, between the substrate and the reaction chamber side, may beabout 1 mm to about 3 mm.

The maximum gap in which the reactant gas to flows within the reactionchamber, between the substrate and the reaction chamber side, may beabout 2 mm to about 15 mm.

The maximum gap in which the reactant gas to flows within the reactionchamber, between the substrate and the reaction chamber side, may beabout 3 mm to about 6 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view representing a gas flowing in the caseof a circular substrate in a lateral flow ALD reaction chamber.

FIG. 2 is a graph representing the most suitable gas velocity for usingthe minimum quantity of gas in the case of a 300 mm circular substratein a lateral flow ALD reaction chamber, as a function of position acrossthe width of the substrate perpendicular to the direction of gas flow.

FIG. 3 is a schematic cross-sectional view of an exemplary lateral flowALD reactor, including a plurality of reactant inlets, where aceiling-defining member is an RF electrode under a flow control plate.

FIGS. 4A and 4B are perspective views of upper and lower gas flowcontrol plates in accordance with the embodiment of FIG. 3.

FIG. 4C is a plan view of one example of a lower gas flow control platethat serves as a ceiling-defining member in a reaction chamber of an ALDapparatus according to an exemplary embodiment of the present invention.

FIG. 6 is a schematic, partially cut-away perspective view of thereactor of FIG. 3.

FIG. 6 is a graph representing the dimension of a gap (reactor height)in a reaction chamber of an ALD apparatus according to an exemplaryembodiment of the present invention, as a function of position acrossthe width of the substrate perpendicular to the direction of gas flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

As those skilled in the art would realize, the described embodiments maybe modified in various different ways, all without departing from thespirit or scope of the present invention.

Now, an exemplary embodiment of the present invention will be describedin detail with reference to accompanying drawings.

Firstly, a gas flux on a round substrate having an actual surface areathat is different from a planar surface would have on the same substratewill be described with reference to FIG. 2.

FIG. 2 is a graph representing the most suitable gas velocity for usingthe minimum quantity of gas in the case of a circular substrate in alateral flow ALD reaction chamber. In FIG. 2, three cases surfaceenhancement factor (SEF)=1, SEF=10, and SEF=50 are represented such thatthe case SEF=1 represents a circular substrate having an actual surfacearea that is the same as a planar surface substrate, the case SEF=10represents a circular substrate having an actual surface area that isten times as large as a planar substrate, and the case SEF=50 representsa circular substrate having an actual surface area that is fifty timesas large as a planar surface substrate. Here, the circular substrate hasa diameter of about 300 mm.

If the gas is supplied in a constant flux and a constant flow velocity,adsorption or surface reaction on the reaction chamber and on thesubstrate may be completed by using a minimum quantity of gas, and thetime required for supplying gas to form a thin film may be minimized inthe case of a circular substrate having an actual surface area that isthe same as a planar substrate. However, when using a circular substratehaving an actual surface area that is at least ten times or fifty timesas large as a planar substrate, more reactant gas should be supplied tothe middle portion of the substrate. If gas velocity over the circularsubstrate is maintained as shown in FIG. 2, adsorption or surfacereaction of the reactant gas in each position 300X, 300W, and 300Z shownin FIG. 1 can be completed simultaneously, and thus no reactant gas iswasted and the time to supply the reactant gas is minimized.

Now, a reaction chamber of an ALD apparatus according to an exemplaryembodiment of the present invention will be described in detail withreference to FIGS. 3-6. It will be understood that FIGS. 3-6 representonly one example of a lateral flow, cross-flow or horizontal flow ALDreactor. The separate reactant inlets to the chamber is a structureparticularly beneficial for ALD, in order to keep reactants from mixingin the vapor phase. However, the non-uniform gap described below is alsobeneficial for other cross-flow ALD reactor designs, such as that ofU.S. Pat. No. 6,562,140, the disclosure of which is incorporated hereinby reference. Accordingly, certain details of the reactor of FIGS. 3-6are omitted in the description below. Further details are provided inU.S. Patent Publication No. 2006/0249077 A1 with reference to FIG. 2-4and paragraphs 27-50, the disclosure of which is hereby expresslyincorporated herein by reference.

FIG. 3 illustrates an ALD reactor 200 according to one embodiment. TheALD reactor 200 includes a reactor cover 201, a reactor base 202, areactor base driver 292, a gas flow control guide structure 205, and anouter wall 298. The reactor cover 201 and the reactor base 202 are inreversible sealing contact with each other and define a reactionchamber. The reaction chamber includes a reaction space 251 in which asubstrate 250 is processed. The reaction space 251 is defined between anupper surface of the reactor base 202 and a lower surface of the gasflow control guide structure 205. The reaction space 251 includes anupstream periphery 251 a into which a reactant is introduced and adownstream periphery 251 b from which excess reactant and reactionby-products are exhausted. The reactor base 202 is detachable from thereactor cover 201 for loading or unloading a substrate 250. The outerwall 298 is configured to pressure-tightly house the reactor cover 201and the reactor base 202, and can be evacuated through an outer exhaust299 connected to a vacuum pump.

The reactor cover 201 includes first and second inlets 210 and 212, andan exhaust outlet 220. The reactor cover 201 is preferably formed of ametal. In certain embodiments, the reactor cover 201 may be formed of aceramic material.

The first and second inlets 210 and 212 preferably extend through thetop plate 203. The inlets 210 and 212 are in fluid communication withreactant sources (not shown). The first and second inlets 210 and 212are configured to supply a first reactant X and a second reactant Y,respectively. Preferably, the reactants X and Y are introduced in vaporphase through the inlets 210 and 212. Valves may be located upstream ofthe inlets 210 and 212 to control the flows of the reactants and theinert gas. For example, 3-way valves can be used to switch gas supplybetween the inert gas and the reactants for each of the inlets 210 and212. In addition, the ALD reactor 200 preferably includes a switchingmechanism for controlling the valves. In one embodiment, a computer isprogrammed and used to alternate supplies of the reactants and the inertgas to achieve ALD sequences.

The reactor cover 201 also includes the cover heater 230 on outersurfaces of the reactor cover 201. The cover heater 230 is configured toresistively heat the reactor cover 201 to a predetermined temperature soas to prevent a reactant from condensing on an inner surface of thereaction cover 201.

The reactor base 202 includes a substrate holder 260 and a substrateheater 270. The substrate holder 260 is configured to support asubstrate 250, and preferably has a recess to secure the substrate 250and expose only a top surface of the substrate 250. The substrate heater270 is integrally attached to a lower surface of the substrate holder260, and is configured to heat the substrate 250 to a predeterminedtemperature, preferably below the reactants' thermal decompositiontemperatures and above the reactants' condensations temperatures, duringa deposition process. The substrate holder 260 is formed of a metal, andis preferably electrically grounded. A skilled artisan will appreciatethat the structure and material of the reactor base 202 can be varied,depending on the design of a reactor.

The reactor base driver 292 is configured to move the reactor base 202in a vertical direction, using a driving device (not shown) such as amotor. Before or after a deposition process, the reactor base 202 ismoved down, and is detached from the reactor cover 201 so that thereaction chamber is open. The substrate 250 can be loaded or unloaded byrobotics through a gate valve (not shown) in the outer wall 298.

The gas flow control guide structure 205 includes an upper gas flowcontrol plate 240 and a lower gas flow control plate 242. As illustratedand described in more detail with respect to FIG. 4C below, the lowergas flow control plate 242 serves as a ceiling-defining member or partfor the reaction space and includes a depression 244 or concavityextending away from the substrate holder 260, and hence away from thesupported substrate 250. The illustrated depression 244 extends in atubular fashion in the direction into and out of the page, such that thegas flow sees the same gap height along the direction of gas flow.

The upper gas flow control plate 240 is stacked over the lower gas flowcontrol plate 242. A central portion of the upper gas flow control plate240 is attached to an inner bottom surface of the reactor cover 201. Inother embodiments, the gas flow control guide structure 205 may furtherinclude additional gas control plates, depending on the number ofreactants supplied into the reactor. The gas flow control plates 240 and242 can be assembled into and detached from the reactor cover 201. Thisconfiguration allows easy maintenance and cleaning. In certainembodiments, however, the gas flow control guide structure may beintegrally formed with the reactor cover 201 rather than havingdetachable gas flow control plates described above. The gas flow controlguide structure 205 defines a first inflow channel 211, a second inflowchannel 213, each of which maintains a separate flow path to thereaction space 251, and an outflow channel 221.

In another embodiment (not shown), a plasma-generating electrode isconfigured to generate plasma in the reaction space 251 during adeposition process, as disclosed in the incorporated U.S. PublicationNo. 2006/0249077 A1 at paragraph [0040]. In this case, the electrode canbe formed as part of over the lower surface of the lower plate 242, inwhich case the electrode can serve as the concave ceiling-definingmember. The plasma-generating electrode may also or alternativelygenerate plasma for cleaning the reaction chamber.

Referring to FIG. 4A, the upper gas flow control plate 240 has first andsecond grooves 241 a and 241 b tapered toward its central portion. Inother words, the grooves 241 a and 241 b widen toward edge portions ofthe upper gas flow control plate 240 as they extend from the centralportion to the edge portions. The illustrated grooves 241 a and 241 bare in a form of a sector of a circle. The first groove 241 a defines afirst inflow channel or passage 211 (FIG. 3) with a portion of an innerbottom surface of the reactor cover 201 for the reactant X suppliedthrough the first inlet 210, as shown in FIG. 3. The second groove 241 bdefines an outflow channel or passage 221 (FIG. 3) with another portionof the inner bottom surface of the reactor cover 201 for excess reactantand reaction by-products, as shown in FIG. 3. The upper gas flow controlplate 240 also has a through-hole 245 vertically penetrating the uppergas flow control plate 240. The through-hole 245 is configured to be influid communication with the second inlet 212 (FIG. 3) and a groove 246(FIG. 4B) of the lower gas flow control plate 242 which will bedescribed below. The upper gas flow control plate 240 may be formed of ametallic or ceramic material.

The upper gas flow control plate 240 also includes a solid part 240 abetween or around the grooves 241 a and 241 b. The solid part 240 aforms sidewalls of the grooves 241 a and 241 b, and is configured toforce the flow outward from the first inlet, around a plate periphery,through the reaction space, around another plate periphery, and inwardto the exhaust outlet.

Referring to FIG. 4B, the lower gas flow control plate 242 has a groove243 tapered toward its central portion. The groove 243 is in a form of asector of a circle. The groove defines a second inflow channel 213 (FIG.3) with a lower surface of the upper gas flow control plate 240 for thereactant Y supplied through the second inlet 212, as shown in FIG. 3.Referring back to FIG. 4B, the groove 243 further extends to a centralgroove 246 of the lower gas flow control plate 242 so that the secondinflow channel 213 is in fluid communication with the second inlet 212via the through-hole 245 of the upper gas flow control plate 240. Inaddition, a lower surface of the lower gas flow control plate 242 and anupper surface of the substrate holder 260 define the reaction space 251in which the substrate 250 will be processed. A non-uniform gap betweenthe lower gas flow control plate 242 and the substrate holder 260 may beadjusted to provide an optimal volume. In one embodiment, thenon-uniform gap between the lower gas flow control plate 242 and thesubstrate 250 averages between about 1 mm and about 10 mm. A skilledartisan will appreciate that the shapes and structures of the grooves ofthe gas flow control plates 240 and 242 may be varied, depending on thedesign of a reactor.

The lower gas flow control plate 242 also includes a solid part 242 aaround the grooves 243 and 246. The solid part 242 a forms sidewalls ofthe grooves 243 and 246, forcing the flow outward from the second inlet,around a plate periphery, through the reaction space, around anotherplate periphery, and inward to the exhaust outlet defined by the uppergas flow control plate 240.

Referring to FIGS. 3 and 4A, the outflow channel 221 defined by thesecond groove 241 b of the upper gas flow control plate 240 narrows asit extends inwardly toward the exhaust outlet 220. Thus, reactant gasesmay react with each other or be deposited on walls in a bottleneckregion B near the exhaust outlet 220 if the gas flow is restricted inthe region B. In one embodiment, a cross-sectional area of the exhaustoutlet 220 is equal to or greater than a total cross-sectional area ofthe first and second inlets 210 and 212. In addition, a cross-sectionalarea of the outflow channel 221 is preferably configured to be equal toor greater than a cross-sectional area of either of the inflow channels211, 213, and more preferably greater than a total cross-sectional areaof the first and second inflow channels 211 and 213. As best seen fromFIG. 3, the top plate 203 of the reactor cover 201 is thinner on theexhaust side compared to the inlet side, creating a high-ceilingedoutflow channel 221. These configurations alleviate stagnation of theexhaust gases in the bottleneck region B and thus minimize the undesiredreaction or deposition.

FIG. 5 illustrates flows of reactants and exhaust gases within thereactor 200 during its operation. At a deposition step, the reactant Xis supplied through the first inlet 210 while an inert gas is suppliedthrough the second inlet 212. The reactant X passes through the firstinflow channel 211, while being spread into a fanned and flattened flowshape. The reactant X then turns downward at the edge of the upper gasflow control plate 240 toward the upstream periphery of the reactionspace. The inert gas flows out from the second inflow channel 213 in amanner similar to that of the reactant X. The inert gas prevents thereactant X from entering the second inflow channel 213. The flow of thereactant X continues toward the reaction space and arrives at theupstream periphery of the reaction space. As shown in FIG. 5, becausethe grooves 241 a and 213 for the reactant X and the inert gas have widemouths in fluid communication with the reaction space underneath theseplates, the reactant X and the inert gas are widely spread when enteringthe reaction space. This configuration facilitates uniform deposition ofthe reactant on the substrate 250.

Then, as shown in FIG. 3, the reactant X flows over the substrate 250 ina horizontal direction from the upstream periphery 251 a toward thedownstream periphery 251 b through the reaction space 251. At thedownstream periphery 251 b, exhaust gases such as excess reactant X, theinert gas, and any reaction by-products, flow upward through a verticalexhaust passage 222 toward the exhaust outlet 220. The exhaust gasesflow through the outflow channel 221 and exit through the exhaust outlet220. As shown, the exhaust outlet 220 has a considerably larger width ordiameter than either of the inlets 210, 212, and preferably larger thanthe sum of their cross-sectional areas.

Referring back to FIG. 5, in a subsequent pulse, the reactant Y issupplied through the second inlet 212 while an inert gas is suppliedthrough the first inlet 210. The reactant Y travels through the verticalthrough-hole 245 of the upper gas flow control plate 240 and the centralgroove 246 of the lower gas flow control plate 242 to the second inflowchannel 213. Then, the reactant Y continues to flow toward and throughthe reaction space 251 (FIG. 3) in a manner similar to that of thereactant X described above. The inert gas flowing out from the firstinlet channel 211 prevents the reactant Y from entering the first inflowchannel 211.

In an exemplary ALD method of depositing a thin film using the reactor200, the reactant X is supplied through the first inlet 210 while aninert gas is supplied through the second inlet 212. The reactant X isguided by the first inflow channel 211 into the reaction space 251 whilebeing prevented from entering the second inflow channel 213 by the inertgas. This causes the reactant X to be adsorbed onto a substrate 250positioned in the reaction space 251. The step is preferably conductedfor a sufficient period of time to saturate the substrate surface withreactant X. Desirably, the adsorption is self-limiting to no more than amolecular monolayer. Next, excess reactant X and any reactionby-products are purged (or otherwise removed). The preferred purgingstep is conducted by supplying a purging or inert gas through both ofthe first and second inlets 210 and 212.

Subsequently, the reactant Y is supplied through the second inlet 212while an inert gas is supplied through the first inlet 210. The reactantY is guided by the second inflow channel 213 into the reaction space 251while being prevented from entering the first inflow channel 211 by theinert gas flowing out from the first inflow channel 211. This causes thereactant Y to react with adsorbed species or fragments of reactant X onthe substrate 250. Reactant Y is supplied for a sufficient period oftime so that the adsorbed monolayer is completely reacted.

Next, excess reactant Y and any reaction by-products are purged. Thispurging step is conducted by supplying a purging or inert gas throughboth of the first and second inlets 210 and 212. Then, if additionaldeposition is required, the above sequence of steps is repeated in aplurality of cycles. Preferably, the steps are sequentially repeated atleast 5 times. Otherwise, the deposition is completed. During the stepsdescribed above, the valves located upstream of the inlets 210 and 212are used to control supplies of the reactants and inert gas.

In another embodiment, an ALD method may start with a non-adsorbingreactant. In certain embodiments, additional reactants may be used forfilm formation. For example, the substrate surface may be treated withan initial surface treatment agent, e.g., water or otherhydroxyl-forming agent, prior to supplying the reactant X into thereaction space. A reducing species may also be used in each cycle tostrip ligands, which help make the process self-limiting, from adsorbedspecies. In addition, additional reactants that contribute to film maybe used in each cycle or every few cycles.

In order to conduct the process explained above, the ALD reactor 200preferably includes a control system. The control system controls thesupplies of the reactants and inert gas to provide desired alternatingand/or sequential pulses of reactants. The control system can comprise aprocessor, a memory, and a software program configured to conduct theprocess. It may also include other components known in the industry.Alternatively, a general purpose computer can be used for the controlsystem. The control system automatically opens or closes valves on thereactant and inert gas lines according to the program stored in thememory.

As noted, the non-uniform gap for a lateral or horizontal flow ALDreactor is preferably used for depositing by ALD on high topography orsurface area substrates (e.g., when depositing into high aspect ratioDRAM capacitor structures, such as deep trenches in the substrate). Thenon-uniform gap is of particular benefit if deposition using reactantswith naturally low vapor pressure, as are commonly used in ALD ofmetallic substances, such as metals, metal oxides, metal nitrides andmetal carbides. Reactants can often have vapor pressures, as measuredunder standard conditions (room temperature and atmospheric pressures)of less than about 0.1 mmHg. Optimal efficiency in use of ALD reactantsis particularly important when using such low vapor pressure reactants,because otherwise saturation of high surface (greater than 10 or evengreater than 50 times planar surfaces) substrates would take aninordinate amount of time, since it is difficult to deliver sufficientreactants of low vapor pressure.

FIG. 4C is one example of a lower gas flow control plate 242 included ina reaction chamber of an ALD apparatus according to an exemplaryembodiment of the present invention. Referring to FIG. 4C, the reactionchamber of the ALD apparatus according to an exemplary embodiment of thepresent invention includes a lower gas flow control plate 242. The lowergas flow control plate 242 has a depressed middle portion 244 as shownin FIG. 4C. Accordingly, the reaction chamber does not have a uniformgap at a portion facing a substrate 250 installed therein such thatparts corresponding to middle portion of the substrate 250 and theportion adjacent to the middle portion are depressed to have widespacing from the substrate 250 in the middle portion of the substrateand the regions immediately adjacent to the middle portion. In this way,the reaction chamber, and particularly the reaction space 251 betweenthe gas flow control plate 242 and the substrate 250, has a tunnel- ortubular-shaped gas flowing section and has different heights at aportion facing the middle portion of the substrate 250 and a portionadjacent to the middle portion from other portions, and thereby muchmore reactant gas may flow on the middle portion of the substrate 250.

In the reaction chamber of the ALD apparatus according to an exemplaryembodiment of the present invention, the maximum gap or height ofgas-flowing space over a circular substrate can be at least one and ahalf times that of the minimum gap or height over the substrate. Morepreferably the maximum gap of space height can be at least two timesthat of the minimum gap over a circular substrate. The ceiling of thereaction space, which controls the gap height, is defined by the lowergas flow control plate 242 in the embodiment of FIGS. 3-5. The lower gasflow control plate 242 of FIG. 4C can also be provided with a uniformlythick RF electrode conforming to the depression 244. In other cross-flowreactors, such as the reaction chamber of U.S. Pat. No. 6,562,140, anupper plate 9 can include a depression that partially defines theceiling of the reaction space (see FIG. 3 of the '140 patent).

The minimum gap or space height, preferably near the side edges of thesubstrate, may be about 0.5 mm to 5 mm, and more preferably about 1 mmto 3 mm in the reaction chamber of the ALD apparatus according to anexemplary embodiment of the present invention. The maximum gap or spaceheight, preferably near the middle of the substrate, and between leadingor trailing edges of the substrate with respect to the gas flow, may beabout 2 mm to 15 mm, and more preferably about 3 mm to 6 mm in thereaction chamber of the ALD apparatus according to an exemplaryembodiment of the present invention.

FIG. 6 is a graph representing gap (reactor height) between a circularsubstrate and a ceiling-defining part of the reaction chamber, such asthe lower gas flow control plate 242 shown in FIGS. 3-5, or an RFelectrode. In FIG. 6, three cases SEF=1, SEF=10, and SEF=50, arerepresented such that the case SEF=1 represents a circular substratehaving an actual surface area that is the same as a planar substrate,the case SEF=10 represents a circular substrate having an actual surfacearea that is ten times larger than the planar surface area of a planarsubstrate, and the case SEF=50 represents a circular substrate having anactual surface area that is fifty times as large as the surface area ofa planar substrate.

Now, a difference in gas inflow according to the height difference fromthe substrate in the reaction chamber will be described in detail.

In the case that gas flows by a difference in pressure between thereaction chamber gas inlet and the gas outlet, the flux of gas isgenerally proportional to the third power of the gap or height of spacethrough which gas flows if the space has a constant height in thedirection parallel to the flow of gas and the space has a differentheight in the direction perpendicular to the flow of gas. Accordingly,in the reaction chamber of the lateral flow ALD apparatus, the speed ofgas flow is faster in portions of gas flow spaces having a greaterheight from the surface of the substrate, compared to the speed inportions of gas flow space having a low height.

A quantity of gas supply to a circular substrate in the reaction chamberof an ALD apparatus according to an exemplary embodiment of the presentinvention will be described in detail with reference to FIG. 6.

Referring to FIG. 6, the reaction chamber of the ALD apparatus accordingto an exemplary embodiment of the present invention includes a lower gasflow control plate (or other ceiling defining member) having a depressedmiddle portion as shown in FIG. 3 or 4C, such that parts correspondingto the middle portion of the substrate and the portion adjacent to themiddle portion are depressed to have larger gap of space height in themiddle portion of the substrate and the portion adjacent to the middleportion. “Middle portion” as used here, refers to the central area ofthe substrate as viewed in a cross-section taken perpendicular to thedirection of gas flow, which cross-section is represented by the graphof FIG. 6. In the illustrated embodiment, this cross-sectional height isconstant from front to back of the substrate in the direction of gasflow.

As shown in FIG. 6, when a circular substrate having an actual surfacearea that is at least ten times or fifty times as large as a planarsubstrate is installed in the reaction chamber according to anembodiment of the present invention, more reactant gas is supplied tothe middle portion of the substrate such that the gas flows similarly tothe most suitable gas supply flux shown in FIG. 2 in a lateral orcross-flow ALD reaction chamber.

That is to say, the most suitable gas supply flux shown in FIG. 3 may berealized in the reaction chamber of the ALD apparatus according to anembodiment of the present invention including a reaction spaceceiling-defining part or member having a depressed middle portion inorder to have wide spacing from the substrate in the middle portion ofthe substrate and the portion adjacent to the middle portion, as shownin FIG. 3 or 4C.

For example, when a thin film is formed on the substrate having anactual surface area that is at least fifty times as large as the surfacearea of a planar substrate, the gas supply cycle required for depositingthe thin film may be completed in the minimum time even though reactantgases are supplied at the minimum quantity required to form the thinfilm by using the reaction chamber of the ALD apparatus according to anembodiment of the present invention as shown in FIG. 6.

As described above, according to the reaction chamber of the ALDapparatus according to an embodiment of the present invention, when athin film is formed on a substrate having an actual surface area that islarger than a planar substrate of the same size, the time required forsupplying reactant gases and a waste of reactant gases may be reduced tothereby increase productivity of the ALD apparatus.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of conducting atomic layer deposition (ALD), comprising:providing a substrate in a reaction chamber; and alternately andsequentially supplying at least two ALD reactants into the reactionchamber space over the substrate in a gas flow direction parallel to thesubstrate, wherein the reaction space has a concave ceiling with atubular shape such that the reaction space has a height over a center ofthe substrate greater than a height over edges of the substrate in across-sectional view perpendicular to the gas flow direction, and suchthat the reaction space has substantially the same height along the gasflow direction, wherein the height over the center and the height overthe edges are such that a maximum gas flow over the substrate is overthe center, and a minimum gas flow rate over the substrate is over theedges, and wherein gas flow rates decrease in the directionperpendicular to the gas flow direction from the maximum flow rate overthe center to the minimum flow rate over the edges.
 2. The method ofclaim 1, wherein providing the substrate comprises providing a partiallyfabricated substrate with a surface area at least 10 times a surface ofa similarly sized planar substrate.
 3. The method of claim 1, whereinproviding the substrate comprises providing a partially fabricatedsubstrate with a surface area at least 50 times a surface of a similarlysized planar substrate.
 4. The method of claim 1, wherein the reactionspace has a maximum height over the substrate and a minimum height abovethe substrate, wherein the maximum height is at least 1.5 times theminimum height.
 5. The method of claim 1, wherein the reaction space hasa maximum height over the substrate and a minimum height above thesubstrate, wherein the maximum height is at least 2 times the minimumheight.
 6. The method of claim 1, wherein a gap between one of the edgesof the substrate and the concave ceiling is between about 0.5 mm andabout 5 mm.
 7. The method of claim 6, wherein the gap between the one ofthe edges of the substrate and the concave ceiling is between about 1 mmand about 3 mm.
 8. The method of claim 1, wherein a gap between thecenter of the substrate and the concave ceiling is between about 2 mmand about 15 mm.
 9. The method of claim 8, wherein the gap between thecenter of the substrate and the concave ceiling is between about 3 mmand about 6 mm.